William H. Slack
Extension Landscape Architect
March, 1990
Buying a new house or building your dream house is an exciting venture. The site you select and its trees will play an important part in the beauty and value of your home and the feeling of well-being it provides for you. Examine the trees on the site carefully and do not overlook the many values they provide.
There are several things to look for when selecting a wooded house site or buying a house on a wooded lot. Some things will cost you money in the short-run, others over the long-run. A little observation and tree care in the beginning can prevent heartache and protect property values while minimizing liability problems.
Real lots are a combination of advantages and disadvantages. The perfect lot does not exist. This publication provides some guidelines to help in the selection of a forested house site and to promote tree health on the site.
There are two types of situations involving the purchase of wooded house sites. The first situation is selecting a wooded lot and having a home built on it. What things should you look for when choosing a good wooded lot for home construction? The second situation is buying an existing home on a wooded lot. What forested landscape items should you look for on such a site?
Effective tree density can be determined by the number of trees per acre for a given diameter class. For example, a lot could be fully occupied by 500 trees one inch in diameter or by 40 trees 26 inches in diameter. There is a trade-off between the number of trees and their diameters for site occupancy. A site will hold only a certain amount of leaf surface, which can be concentrated into a few large trees or distributed among many small trees. (See diagram A.)
One way to estimate tree density is by measuring basal area. Basal area is the cross-sectional area (in square feet) of all the trees on an acre at 4.5 feet above the ground. A wooded house site is overstocked if the basal area is greater than 80 square feet, and is understocked if the basal area is less than 40 square feet. Basal area of between 40 and 80 square feet is needed to maintain a wooded character. Contact a forester for easy ways to measure basal area.
If there are too many trees, each tree has a greater chance of being unsound or unhealthy. If tree cover is sparse, each tree may be healthy, but the site may have soil limitations restricting growth. Sparse growth may indicate that the site was cleared of desirable trees, leaving only the less desirable ones.
Sites with trees of only one age group or size may be beautiful, but if a disease or insect attacks, the entire tree cover could be lost in one season. The greater the variety of sizes and species you have, the healthier your wooded site can be. Thin existing trees, plant new ones, and plant and protect seedlings from damage for a healthy forested look.
If the live crown is less than 20 percent of the total height, the tree should be removed before construction begins. If half of the tree's total height is crown, it has the best chance of surviving construction damage, as well as any future environmental stress. Living crown size is not an accurate measure of a tree's health if other types of mechanical or pest problems occur.
Check for dead branches, especially in species such as oak and hickory, because dead branches in the tree top indicate damage by drought or root problems, and will cause liability problems.
Examine the bottom 20 feet of the trunks for scrapings, bark tears, or open wounds. Minor injuries will not hurt a tree, but extensive damage on a large number of trees means the site was poorly taken care of when thinned or logged. Damage will lead to many problems in the future. Consider eliminating trees with extensive damage. If mechanical injury disrupts more than one third of the tree's circumference, remove the tree.
Also check for main stem damage high in the tree. Stem faults such as fusiform rust cankers on pine can be points of breakage in storms. A tree must be mechanically and biologically sound to live a long life near a house. Another thing to look for on many sites is "high-grading", which means the best trees have been removed, leaving only crooked, diseased and poor species of trees. Buying a lot that has poor quality and misshapen trees or undesirable tree species may mean the good trees were removed by logging.
On hilly land there are pockets where soils are deep, rich and moist. There are also pockets where soils are stony, fragile and shallow. Deep soils are usually better than shallow soils for tree growth and minimizing construction damage to trees. shallow soils and the trees growing on them can be damaged easily by construction. On steeper slopes, the soil is thinner so the potential for soil erosion is greater. Avoid injury to trees by minimizing soil disruption and clearance on steep slopes and shallow soils.
On hilly terrain, the landscape consists of hilltops, hillsides and valley bottoms. Each area will grow trees of different species and qualities. Tree growth is usually best in valley bottoms. Bottoms frequently have deep moist soils and are excellent places for tree growth if flooding is not a problem.
As you move up a slope to the hillside, soils tend to become more shallow and tree growth is poorer. Hilltops and ridgetops receive the most sun and wind, and water runs away from these sites quickly, resulting in poor tree growth. Coves, sheltered areas with pockets of good trees, are scattered over hilly terrain. Coves support strong tree growth if they are not excessively disturbed.
On flat sites, the major concern is poor soil drainage rather than erosion. When property has little slope, even a very minor grading change can alter water runoff patterns. This can result in standing water after a rain. Certain species of trees have low tolerance for continuously wet soils or flooding. If construction activities alter water flow through the site or cause pending on the site, the health of some trees will be jeopardized.
The floor of an undisturbed forest will have a layer of leaves, needles, sticks and branches called litter. This litter is a natural mulch that helps protect the soil surface. If litter is present, it means the site has sustained few adverse soil changes. If the litter layer does not exist, soil disturbances, compaction and clearing may have already occurred and the trees will be susceptible to further root and stem damage.
Take your house plans, a 100-foot tape measure, a compass, string and some stakes to your lot and outline where your house, drive, patio and sidewalks will be on the site.
This will help you visualize what trees will have to be removed. If a tree is within 30 feet of the house, it is in the construction danger zone and should usually be removed to ease construction. Trees left in this zone can eventually become a hazard to the house and yard. (See diagram D.)
Quality trees within 60 feet of the house, especially those 30 to 60 feet from the house, are in the tree protection zone. Trees at risk of damage or of poor form should be removed. Trees need special protection in this area, so if a tree is damaged during construction, it may need to be removed. Prevent any construction activities beyond 60 feet of the house.
To minimize damage to trees within the tree protection zone and beyond, a protection barrier is essential. Whether a temporary wooden fence or a wire with flagging is used, be sure the fence is in place before construction begins. The protection barrier should be freestanding and located where it will guard the trunk and the surrounding ground surface. Protect two-thirds or more of the drip line of the tree. Barriers will not prevent all damage but will remind people working around a site that trees are important and that the barriers should be respected.
It is important for building contractors to assess what effects grading will have upon the drainage of the property before any site disruption begins. Proper planning and consultation with construction personnel and tree specialists can minimize many tree problems.
Always limit construction machine access, material storage, fuel tanks, chemical or cement rinsing, vehicle parking and site-office locations to non-tree areas. Keep construction equipment away from the trunk or main rooting area of trees to be saved.
In an ideal situation, you would own a lot several years before construction begins and perform preventive maintenance before construction to safeguard trees. Proper pruning one or two growing seasons before construction can eliminate unwanted or dead limbs and branches in hazardous positions. Mulching can help prevent erosion, soil compaction and root damage when construction begins. Spreading bales of pine straw, pine bark, or aged wood chips can supplement the natural litter on the forest floor.
Always plan access corridors for underground and overhead utility installation. Provide room for trucks and construction equipment to get to the building site. Do not put up barriers that limit access to the building site. Make it easy on yourself, your trees and the construction crew by being realistic and knowledgeable about when to save trees and how to protect them.
Look at tree crown size. How wide-spreading are the crowns? Are there dead limbs or dead branch stubs in the trees? If so, decay may be well-established and the trees could soon become a liability. Make sure that the trees have at least 33 percent live crown. Ideally, half the height of the tree should be living crown. Also check the variety of tree species present and their sizes. Look for a mix of large, medium, small and seedling trees.
Check carefully for trunk damage such as scrapes, vertical cracks, branch stubs, improper pruning, lawnmower/machine damage and bark tears. These are signs of tree abuse that can lead to tree decline and death.
A tree with a lot of trunk suckers or sprouts (shoots coming through the bark along the trunk and major branches) is a site risk. Suckering is a sign of root damage and tree decline, so trees with suckers should probably be removed.
Contact a professional arborist or urban forester for an evaluation. Using professionals that deal with these problems every day can save you time, effort and money. Current and accurate information is essential for making wise tree decisions.
With timely attention and proper maintenance, you can keep your trees healthy and vigorous. Protect trees by keeping machinery away from them and by protecting the soil surface and its natural mulch, and you will benefit over the long run.